Testing system for party-lines.



UNITED s'rn'rns PATENJ. OFFICE.

. DWIGHT A. LAwvER Ann CLIFFORD c. BRADBURY, or CHICAGO, ILLINOIS, ASSIGNORS TO KELLOGG'SWITCHBOARD AND SUIfPLY COMPANY, or czr rcaeo, ILLINOIS, A COR- IPUL E-A'IIOLT OF. ILLINOIS.

r H TESTING SYSTEM FOR PARTY-LINES.

To all whom it may concern;

Be it known that we, Dw1o1rr A. Lawvnn I and" Currono C. .Bn'apnuki'; citizens of the United States, residin in Chicago county of Cook, and State, of I linois ,have'1nvented certain 118W and useful Improvements .in 'Testin the fol oymngis a specification. v

Our invention. relates to telephone 's'ys' Systems 'for Party-L nes, of which tems, and particularlyto' the means, f'testing the idle (ll-busy eonditionoftlefihoiie' of lgno winggwliethei' lines-having aplurality of substations coninedfld thereon.

'sy'stem" it i the s. sp e ete s i s comm' on'-- prac' tice'to" esignate each, substation by a. inber,

no'metter whether, there but one" or sulistation is connected iiponlt he sanilinewith his own. In telephone-.systems of; the' cqmmon. .bat-te or energy it is ordinarily impossible to sound the annunci-atorlht one of the substationsupona tel phone 'line while thereeeive'r m nomer substation'upon the-same line is off the switch-hook. It, therefore, becomes necessary when onersubscriber' desires-another subscriber on the same linefor. theopetator;

' to request the calling subscriber to replace his receiver upon theswitclt hook .until thedesired subscriber has been called.

In order that the operator will know that the desired substation is located upon the same telephone linewith the calling substantion, we provide means for producinga distinctive, tone which shall be heard by the operator only .When' she is testing one of the multiple jacks of the same line which is calling. a An arrangement has been-proposed to operate with a system using three conductor'cords and three conductor multi 1e jacks; and it isthe object of the present-1nvention to produce an arrangement which may be successfully operated in connection with two conductor cord circuits,- and it is the further object of our invention to acconiplish the desiredend in a simple, efiicient and economical manner.

Our inventionf is illustrated in the accompanying drawing .which repres'entsa four party telephone line and the connecting Cir Specification of Letters Patent. Patented 113 13, 1910. Application filed lleceniber 1?,1908. 'SeriaL No. 467.940:

cuit for establishing aconnection therewith, all of the apparatnsbein normal orunactuated con ition Each oft-he substations 1, 2, and 4 is provided with the annrinciatot-fi; and condenser 6 in a permanent bridge between the line conductors Fund 8, and with the transmitter 9 and receiver 10 in abridge maintained normally-open by contacts of the switch book 11. At the central ofiice, line conductor 7 is, connectedthrough the contacts lfl and 13 of cut-01f relay 14:, and the coil of line-relay fi with the live pole of battery 16, and lineconductor S'is connected througlrcontacts I'L and 1'8 ,of scut-ofi' relay 'i4 1 g1th earth: "The'line-relay 15 has. the

'd't' ri' l to'ooznpltltethe circixit o the The sleeve, contact 22 of the f ansvveringjaclf is conndtted through" con-j ductor-23 with;.l l 1e..-sleeve contacts "24 ofthe contacts 28 of the multiple 'jacks and also Withthe normally open insi tle contact 29 ,qfi-cut-pflre'lay 145 i 3 The cord circuit for use with this line has tip and'slee've talking strands, the tip strand extending from the tip contact 32 of the answering plug through conductor 33, condenser 34 conductors 35 and 3H and the series contacts of the ringing key 37 to the tip' eo'nlac; 38 of the calling plug, and the sleeve strand extending from the-sleeve contact 40-01 the answering plug through com opencontacts and the relay 'ccntrolling normally closed contacts inthe circuitof said slgnal.

The calling supervisorv relays Q0 and 51,

, open contactslllandilfl ada ted' multiple; aeksi'and also thei' inside contact 25 of cut-oil relay l i'and with the coil of itherelay, 'the other terminal of the coil of said relay being:connecte d with earth 1he t ip contact 26 6f the answering jack is'c'onnested through conductor 27 "with the tip ductorfl, condenser 42, conductor 43 and The answering supervisory relays 45 and' ormallyli sleeve conductor 43 of the calling end of; the cord circuit,- and is adapted. by theacto be connected through nnnal of'thc coil of said nected with earth, Copductgr 60 is also cont -tuation of the key a re similarly conncctcd in a bridge between the tip and sleeve conductors 35 and 43 upon the calling side of condensers 3i and 42, this bridge also containing battery 47. Relays and 51. coiipcrate to control the. circuit of the calling supervisory signal relay 51. controlling normally open contacts and rclay in) controlling normally closed contacts in the circuit of said signal. The relay 51 also controls the contacts 53, 51L and.'55, c0ntacts 53 and 54 maintaining a normal break between the portions 3.3 and 36 of the tip talking strand, and contacts .54- and 55 normally connecting the portion 36 ot' the tip talking strand with conductor 56 which cxtends to the normally open auxiliary contact 57 of the operators ringing key The other normally opsn auxiliary contact 59, adapted to connect with contact 57 when the listening he is actuated; is connected through con actor 60 with the coil o f-the high resistance test relay 6 1, the other terrelay being con nected through the condenser 62 with conductor 63 which is in turn connccted through the tertiary winding 64 of the -o era'tors induction coil with the live pole 0 battery :17.

The spring ing key '58 is directly connected with the contact. 66 with the contacbfii" of test relay 61, and through the normally closed contact 68 of relay 61, condenser 69, secondary 70 of the'operators induction to the contact. '51. of the operators listening key 72 of said key being connected 58, the contact throu h conductor 73 with the ti talking strand 35 of thecord circuit. T e"spring 67 of relayv 61 is adapted to connect with contact; 74 of said relay when the relay is actuated, this contact connecting through conductor 75 and the: secondary 76 of the tone producing transformer to the live pole of battcljn 76, the primary 7? of said transformer and the high frequency current interrupter'7 9 being connected in series with said battery. The operators" receiver 80 is connected in a series circuitwith the. winding 81" of the opcrators induction coil.

The normally disconnected sleeve contacts 85 of the operators ringing key are con nccted in multiple. and through the noninductive resistance 86 and thc battery to carth. The normally disconnccled tip contacts of the operators ringing lacy are connected with the ringing generators 88, 89,, 90 and BL those generators liciug adapted to furnish distinctive current for selectively operating the annuuciaiors at the difi'erent subscribers stations.

In the o a-ratiou of the system thus dc- :srribcd, presuming the subscr bcr in charge 65 of the operators listens i .s-numbcr of the dcsiredline is now of substation l desires another subscriber upon this same line, he removes his receiver 1.0 from the switch hook 11 and thus coniplctcs a circuit from. the live pole of battery 10 through the coil of line relay 15, contacts 13 and 12 of cut-otl relay 14-, line conductor 7, transmitter 9, receiver 10, switch hook 11, line conductor 8 and contacts 17 oil relay 14 to earth. The current in this path actuatcs line' relay tacts J9 and QO'and completing the circuit. of the line signal 21. Upon the display of signal 21 the operator inserts her answering plw into the answering jack designated b t c signal 21,:1and thus completes a circuit from the lire pole of batter 47 through the coil ofsupervisory relay 46, plug and jack'aritlf the coil of cub-ofl' relay 14- to ground The actuation of relay 1,4 connectsithis-t-jlixhbsof the telephone line directly with the'fiiphndislvccontacts of the jacks and interrupts the circuit of the line relay'15, which relay-til sumes its normal condition causm the line signal 21 to be etlaced.

have; c n a n 2210 25 and 12 accorda- 4: 1 conductor 7, transmitter 9 "of the jack and lug in the ooil" of siigci'vi'sory 'rela I ground 'le ot attery 47. I e currEnt-in leaving the supervisory signzi' 48*stil1 in" its etfaced condition. f p f 3 The-operator now actuatesher listening key 58 completinga circuit from the spring 65-through contact 66, contacts 67 a'h'd 68 the operators induction coil,- contacts 71 and 72 of the operators listening key 58, and conductor 73, this circuit being in a bridge of the talking strands of the cord circuit. The obtained in the usual way, the voice currents through windin :ductive y reproduced in windingSl and in receiver 80. The answering and multiple jacks being located in different parts of the switchboard and to one another, the operator thus fa r does not know that. the desired-substation is lo-' catcd upon the same of the calling subscriber. According to, the usual procedure. the operator now lifts her.

tin-sleeve or test contact of one of the multitest contact-ll woulcl ho at a 'iotcntial higher 1 than that of earth. and current would there- 15 closing its-con- I .A circifit is also" oompleted through the coil oflsupervisorye 70 of the inductiontcoil being inand 18 of cut sleeve, contacts 40 and 22 of the 4-5 :to'the this pa actuates bot-h rain. 5 sound 45,-

ofsrela v 61, condenser 69, SecondarvTO' of"- bearing no visible relation telephone line as that calliugplug and touches its tip contact with] hle laQlKs-of the desired suliscribers line. If 7 this line was not that of the calling sub scriher but was otherwise husy. its slceve'or induction coil would cause a click in' 'the ill ators' induction coil to the live pole "of source 78 woul flow through conductor 75,-

6O the operator has thus determined that. the desired subscribers station is located upon tested will be busy due to the fact that the callin end of this same c'ord circuit is conline. The operation of; the test relay 61 will -and".65 j the listening key,58 conductor ceiter whichjs only heard 51, conductor 56, contacts 57 and 59' of the now actuated listening key conductor-6O and through the coil of the high resistance tcst'relay 61 to ground. The current in this i path would cause the actuation ofrela'y 61 and also would cause a discharge of. condenser ('32 which would cause a rush of cu'rrent througlithe .tertia'ry winding 64 of the operators induction coil. The impulse of current through the tertiary of the operators operators receiver which would indicate to her that the line was busy. However in the case here-illustrated the sleeve of the jack necte :withthe answering jack of this same therefore open. iip the circuit of the secondary of the o erators induction coil and will connect the distinctive tone from the secondary 76 of the tone producing transformer through conductor 75, contacts 74 and 67 of test relay'.61,' the'nowfclosedcontacts '66 43, gzoil'gienser 42, ,conductorAl, sleeve contactfsz40 and 22 of-the answering plug and jack; conductor-23, sleeve contact '24 of the inultipldjackgtip.Q n rct 38, conductor 35, contacts 54 asset supervisory relay 5'1,- conductor 56, contacts 57 and 59 of-listening key 58, conductor 60, condenser 62, conductor (33 and the tertiary winding 64 of the operattery l7. Thisdistinet-ive current will-cause a toneto-beproduced in. the operators rewhen the operatortests the multiple 1ack of the same line with which the answering end of her cord circuit is connected.

The particular object of the break con-\- tacts ($7 and 68 ofrelay .61 is to prevent a false signal being'given to the operator when testing abusyline which is not made busy by the connection of the calling end of this particular cord'cireuit with a jack of the line. If contacts 67 and 68' were not interrupted ifa-lse'; test would be received in the follow'in manner :I Current from the contacts 74 and 67 of relay 6.1, from contact 66 to contact 68 which would in this case'be permanently connected, through condenser- 69, winding of the operators inductioncoil,-contaets 7.1 and 72, conductor 73, condoctor 35, the coil of relay- 50 to ground, giving a falsetestto-the operator. \Vhen;

the same line with the calling subseribers station,she informs the calling subscriber of .may be accomplished this condition and asks him to replace his receiyerupon the switch hook until the desired subscriber has been called. As soon as the supervisory signal lta' is displayed, due to the interruption of the circuit through the coil. of relay l5, when the calling subscriber replaces his receiver upon the hook, the operator actuates the proper ringing key to selectively call' the desired snbscribelx.

Before doing this, however. the operator removes her answering plug from its connection with the answering jack so that the ringing currentwill not be shunted tl'zrough the. coil of the answering relay -15. The remaining part of the supervision is accomp'1ishedby'means'of the calling end ofthe cord circuit. Relays 50 and 51 are now bothactuated, th ecurrent for .the transmitters of both of the substations being furnished through the 'coils of these .1 relaysi \Vhen both the subscribers replace theirreceivers upon the hooks, the circuit of relay ho -is interrupted, and this relay' resumes its nor mal position, eompletingthe'circuitof super visory signal 52 which indicates to the operator that the conversation has been terminated.- She therefore removes her calling plug from its connection with the multiple jack and thus interrupts the circuit of relays 51 and 14;..causing "all of the apparatus to return to its normal condition. i It will be noted .that the relay 61, condensers 62-and '69, and the operators induc-- tion coil and receiver are common to all of the cord circuits controlled by one operator and that the tone producer 79 and the trans former associated therewith are'conunon to all ofthe o erators of the exchange. Branch wires are s iown on the drawing to indicate the points at which the testing apparatus becomes common ,to the particular cordcircuit only. The contacts of the listening-key 58 are used in this case to separate the comr mon ap aratus from the particular cord'circuitj t is to be understood that other methods may be adopted for connecting this s ecial a aratus with the cord circuit in use, where y "the advantage of having but one test relay for a plurality of cord circuits and it is to be understood that we do not wish to be unduly lim{ ited to the particular means'here shownfor accomplishing this result. Other modifications of this circuit may be'obviously made a without departing from the spirit onscope of our invention.

We claim:

1. In a testing with a tele ho'ne linahaving a busyv testing. terminal, 0 an operators testing contact for testingthebusy condition of the line, a cord circuit having, its answering end connected with the line, a testing circuit including a portion of the answering end of the sleeve talking strand of said cord circuit closed system.- the combination when a busy line is tested, and a suitable de- 1.30

" use during testing,

opcrators testing cont conductor, a switch for connecting said cin operator-s induction circuit, whereby when said line is tested a special tone is produced in the opcratofs receiver, said device being nm'inall disconnected from the cord circuit by'contacts of vice for interrupting the current flow in said i I the voperator-s listening key, substantially as described. I

In a testingsystem, the combination I with a telephone-line having a busy testing terminal, of a plurality of cord circuits, an act for testing the busy condition of the line, an alternating! current testing circuit, an electronnignetic-j device for connecting said circuit with the sleeve voi ce current conductor when a busy line is tested, a pair of normally open contacts adapted to be clo-ed during testing in i the circuit between thecontacts of said electromagnetic device and the sleeve voice current conductor, whereby asingle magnetic device may be used with a plurality of cord circuits, substantially as described.

3. In a tes tingf;syste1n, the combination with a tele )honeline having .a busy testing terminal, 0 testing the busy condition 'of the line, an oscillating current testing" circuit, a common cuit with said testing, and a said common conductor with strand 'of the particular cord circuit then inwheiehyfsaid first mentioncd switch may be common to a plurality of cord circuits, substantially as described.

4. In a testing system for telephone lines, the combination with a cord circuitin which the sleeve voice current. strandis connected with the test contacts of the line during the connection of the cord with the line, of a special test current source adapted to be connected with the sleeve voice currentstrand during testing, an op'era'tors receiv-- ing circuit bridged between voice current strands of the 'cord circuit, and means to interrupt said r -civing circuit whenever said special test iroducing device is connected with the seeve strand of the curdcircnit to prevent the current from said test producing device from givi a false test to the operator. substantially as described.

5. In a testing system for telephone lines, the combination with a cord circuit having common conductor during anoperators testing contact for W "Cllltffi source second switch for connectingth'e sleeve tip and sleeve voice current strands, of an operatofs induction coil, :1 special test current source adapted to be connected with the sleeve talking strand during testing, the current from said'sonrcc pas ing over the sleeve of the cord circuit, the sleeve contacts 4 of the answering and multiple jacks of a 1 calling telephone line, the tip'of the calling end of the cord circuit and a winding of the coil, and means to pre vent Currem from said SP CHEl test nrndrc- 3 mg device from passing through a winding 1 of the operators induction coil other path, substantially as described.- ,1

6. In a telephone testing systennthe cognbination'with a' cord circuit having t-ipgand sleeve voice current conductors, of 'zuropeg:- ators listening key'associated with the cord circuit, an operators receivingf circuit adapted to. be bridged betweenthe'talking strands of the cord circuitwhen the key is actuated, a source of distinctive current adapted to be connected with the 'slee've of the cord circuit during testing, and means to interrupt the to prevent current from said source from passing through said opera tors receiving cir'- cuit during testing and thereby producing afalse signal in-the 0 erators receiver, substantially asdescribed T. In atesting system for. telephoneilines,

the combination wlth' acord circuit having tip and sleeve voice cu'rrent conductors, of, an operators receiving circuit'bridgedbe tween said conductors?ftir;= conversational purposegnteg t conductpi includijn mgend f the t1 "strand of s a; id;

. of istinctive cu'rr'' to be connected\with the sleeve rent conductorof'sa'id circu if ing plug is touched othe 'test' -'contact of the -same telephone line with-* 'which'the sleeve of theanswering plug is connected, substantially as described. i 8i In a test-in system for telephone party lines; the combination with a. cord circuit having tip and sleeve voic'e current'conductors, o'f a-testing circuit for said cord cit cuit a supervisory relay for th'efcordflcitcuit nc tuatedwhen the callingend'of theco'r circuit is connected with the ja'ckof a telephone line, normally closed contacts of said relay in said testing circuitfan operators listening key, norm-ally open contacts of said listening key adapted to be included in saidtesting circuit during testing a relay hav ing its coil connecte .with-one of said contacts of said listening ltey andadaptedto be actuated by the test current insaid: testing -circuit, a source of distinctive cu 'n'tadapt ed to heconnected with the sleeve voicecurrent condnctor'ofthe cordcircuit by the actnation of said relay, the circuit from said source to the sleeve strand of the cord circult passln through normall open contacts of 831C istemng key, sai relay being adapted to interrupt the operators receivin circuit back of the point at which the distinctive current is connected with the sleeve of the cord circuit, whereby current from'tlie distinctive source will not be heard by the operator during the testing of a line other than th calling telephone line, substantia ly as described.

over anyoperators receiving circuit inggsubstantially as described.

means common to a plurality "sleeve voice current conductors, of a calling 'rality of cord circuits for connecting said conductor of the cord circuit during testtesting, whereby the operator will receive a testing-the b'usy condition of asdescribed. .18. a tie ephone the combination I with a telephone line having a plurality of subscribers connected therewith, of'a plurality of testii'ig terminals connected with one of the talking strands of? said line dur-. in g conversation, a distinctive current source, means for connecting said source with the test contacts of said telephone line during testing, means whereby the operator'may rcceire a signal from said distinctive source when testing one of the multiple acksof said line, and means to prevent theoperator from receiving a signal from said source when testing one of the multiple jacks of another telephone line, substantially'as described.

10. In a telephone testing system, the combinationwith a cord circuit having tip and 9. In a testing system,

line, a distinctive current source adapted to be connected with the sleeve strand of the cord circuit for producing a special test tirhen one of the multiple jacks of the calling line is tested, and a relay common to a pin distinctive current source with the sleeve 115-"1fi' 5 telephone testing system, the combi'nationwith afcord circuithaying tip and sleeve voice current conductors, of a source of distinctive current, a common conductor,

of cord circuits'for. connecting said distinctive source with said cornmoh conductor during testin and means individual to said cord circuit for connecting said common conductor. with the sleeve strand of ,the cord circuit during distinctive current from said. source when testin one of. the multiple of the, call.- ing te ephone line, substantially as described.- 12. In a testin system, the combination with a telephone ine having a busytesting terminal, an operators testm I contact for the line, a dis tinctive current source, an electro-magnetic device common to a plurality of cordcircuits for connecting said source with thesleeve voice current conductor when a busy line is tested, said source being adapted to produce a-special tone in the operators receiver when said line is the calling tele. phone line with which the answering end of the cord circuit is connected, si'ibstantially testing system, the combination wit a cord circuit, of a calling line, a distinctive current source adapt-ed to be connected with the sleeve strand of the cord circuit for \i'o(lucing a special test when one of the multiple jacks of the calllug line is tested, and a relay common to a plurality of cord circuits for connecting said i distinctive"current stun-cc with the sleeve I with a telephone .with a telephone line described.

" testing the busy 'with a telephone ine havin conductor of the cord circuit during testing, substantially as described. 14. In a testing system, the combination ine having a busy testing terminal, of an operators testin for testing the bus condition of t e line,- a testing circuitinc uding a portion of the talking eircuitof the answering end of the cord adapted to be closed when abusy. line contact 70 y is tested, means associated with 'said'circu'it for interrupting tone is produced inthe operators rece ver, and means'whereby a signal of different character will indicate has been tested, substantially as described.

the current flow therein, whereby when saidcircuit is closed a. special when a difierent-line 50 I 15. Ina testing system, the'oombination havingja busy testing telllulldl, of an operators testing contact for testing the busy condition ofthe line, a -cord g5 circuit for makin connectionwiththe'lme, a testing circuit including a portion of the answering'end of the sleeve talking strand closed when a busy line istested, a suitable current interrupterassociated with .said 1cir-- 9 0 cuit for interrupting the current flow theft? in, whereby vhen a bps' line. is .special tonel' fb receiver, said special tone-mdicatlng .t'iifferent condition of the tested lindfromthat indicated, by the usual .test, substantially as p 16. In a testing with atelephone'. i terminal, 0

systerir, combination ne having-a busy testing condition of the line, an alternating current .testing'circuit, tromagnetic device for connecting said'ci'rcuit with thc answering end-of the sleeve an operators testing c'ontact'for 10o el cvoice current condujcton whens-busy line is 10:;

tested, said circuit being adaptedto produce; a special tone in the, operators receiver, and means whereby a si lei-.difiereiitcharacter will indicate w strand of the en a ,diiferent-lincl as been tested, substantiallyas described. 17. In'a testin system, the-combination condition ofthe.

said circuit being adapted to produce a special tone in the openatorsreceiver whe a busy line' is tested,fsaidfjspciall ifidi catin a difi'erent condition ofthc tested line rom that indicated by the usuall test, substantially as described.

18. In a testing system, the combination with a telephone line havm a busy testing teuniual, of a cord circuit or making on-i nection with the line, an operators test ng contact. for testing the busy condition of theanother line, substantial1y as described.

rent tcstin line -a busy 19. In a testing systcm. the combination "with a telephone nection with the line, an operators testing contact associated with the tip strand of the cord circuit for testin r the busy condition of the line, and an induced alternating curcircuit includin the sleeve strand of'te cord circuit and a line condoctor, said circuit being ada ted to produce a special tone in the operator 5 receiver when line is tested, said special tone indicating a different condition of the tested substantially as described. 20. In a testin system witha telephone l terminal, of a cord circuit or making connection with the line, an operators testing contact for testing the busy condition of the line, a direct current testing circuit, an alternating current testin circuit including a sleeve strand of the co circuit and a portion of one line conductor, electromagnetic means for closing both said circuits whena busy line is tested, said alternating cur rent circuit. being adapted to produce a special tone in the operators receiver, and means to prevent the "operator from receiv- .ing a signal from saidtone when using the direct current test, substantially as described. 21. In a system, the combination with a 'lu'rality of substations located upon a telep one line, of a plurality of connecting contacts for said line atthe central ofiicc, a cord circuit, a testing terminal 118-- sociated with said cord circuit, a si nal circuitudapted to 'be closed over sai testing terminal when-said line is in connection with a second curd circuit, a difl'erentsi nal cirthe combination cull/adapted to be closed over said testingterminal and a portion of the tu-lkin unit f the answering end of the cord circuit, when said line is in connection with the answering end of said first cord circuit, said .testing circuits transmitting signals of dif- .ferent .clmracteristic sounds to the o )eratoi,

and means to prevent the operator v rom rcceiriug the last signal when the condition tone when testing ne having a busy testing 1 terminal, of a cord circuit for making con- 5 talking strand of a cord circuit when it is om that indicated by the usual test,

inehav-in a busy testing of the line te ted requires llw operator to receive the first signal only. sul'istanlially 21 described. i

In a leslin sysreuu the combination with a lclu 'ihonc inc, of a plurality of substations upon said line, and a plurality of ,lust contacts for said line al the central ol'lic'c, a cord circuit, a. testing terminal associated with said cord circuit, a signal circuit adapted to he closed over said lusting terminal and the answering end of the sleeve connected with the test contact of the calling line, and means whereby a signal of different character will indicate when a different telephone line has been tested, substantially as described.

2-3. In a testing system, the combination with a telephone line, of a plurality of'suh stations upon said-line, and a plurality of testing contacts for said line at the central otlice, a cord circuit, a testing terminal associated with saidcord circuit, a busy test circuit adapted to be closed when the cord test terminalis connected .to the test terminal of the busy line, 'a tone signnlc-ircuit adapted to be closedfirer a portion of the answering end of the sleeve talking strand when said lintbusy by its C(Hlllt'CtlOIiWVitll the-answering end of said cord circuit," and means to prevent the operator from r ceiving said tone signalwhcn said line is busy hv its connection with another mrdcircuit,

substantially'l as des6ribedi-- 24. Iii a testing system, the combination with a telephone line having a plurality of 5nbscribers"connected therewith, of a pluralit of 'lesting terminals connected with one o! the talking strands of said line during vonynrsa-tion, means for connecting a distiuctivet'an'rent with the test-contact of said telephone line when one subscriber of said line requests connection with asecoud subscriber of the same line, a direct.- .current test adapted to be used when a subscriber on said line requires connection with a subscriber on another line, and meansv to preu-nt the operator from receiving a signal from said distinct current when using the direct current test, substantially as described.

Signed by us at Chicago, county of Cook, and State of Illinois, inlhe presence of two fitnessesz;

Manaonm Fl. Ginsu,

'Eorru F. Gama. 

